Air curtain doorway method and system



Jan. 31, 1967 w, ZUMBIEL AIR CURTAIN DOORWAY METHOD AND SYSTEM 2 Sheets-Sheet 1 Filed April 12, 1966 Jan. 31, 1967 w. A. ZUMBIEL AIR CURTAIN DOORWAY METHOD AND SYSTEM 2 Sheets-Sheet 2 Filed April 12, 1966 ZD/P-I United States Patent Ofitice 3,391,162 Patented Jan. 31, 1967 3,301,162 AIR CURTAIN DOORWAY METHOD AND SYSTEM William A. Zurnbiel, 85 Dudley Road,

South Fort Mitchell, Ky. 41017 Filed Apr. 12, 1966, Ser. No. 549,095 12 Claims. (Cl. -9836) This application is a continuation-in-part of application Serial No. 414,978, filed December 1, 1964.

This invention relates to air curtain doors and more particularly to an improved system for regulating and maintaining a velocity stream of air across a doorway.

Today, air curtains are often used in place of conventional doors in heavily trafiicked buildings such as oflice buildings, department stores, etc. These curtains consist of velocity streams of air, usually operatingin a closed circuit, and operable to keep temperaturized air within the building and un-temperaturized air, flies, etc. outside the building. Because opening and closing of doors is avoided by these air doors, and the air door is maintained at all times, heated or cooled air is retained in the building with a resulting reduction in the cost of maintaining the heating or air conditioning of the buildmg.

These doors are also desirable because they permit free and unobstructed entry through the doorway which they seal. This is particularly advantageous in commercial stores which like to guard against panic in the event of fire or other emergency conditions.

One of severist limitations in the commercial use of air doors has resulted from the velocity limits imposed by people using the door. By way of explanation, the most efficient type of air curtain door is one in which the air stream which forms the curtain, moves at a very high velocity. If this type of high velocity stream is maintained, wind blowing against the air door cannot compromise or break through it. Unfortunately, people or customers of the building using high velocity air doors are just as unlikely to break through it. The primary reason people object to these high velocity air stream doors is that the air is usually heated in the winter and walking into a high velocity stream of heated air is at best an uncomfortable experience. Additionally, women particularly, but not exclusively, do not like to have their hair blown into disarray by the high velocity stream.

The result has been that where closed circuit air doors are used, they are made aproximately six to ten'feet in depth and the velocity of the air stream is held to something humanly endurable but very inefiicient. The six to ten feet of depth is required if the air door is to remain intact against relatively high velocity wind.

As a consequence of the great depth required for air doors, many commercial installations which would enjoy the prestige as well as the heating and air conditioning efficiency of an air door, have been unable to afford them either because they cannot afford to sacrifice this much space or the high cost of these large installations precludes their use.

It has, therefore, been an objective of this invention to make air doors commercially feasible where they have heretofore been impractical. Otherwise expressed, one objective of this invention has been to substantially reduce the dollar cost and sacrifice of floor space heretofore required in a closed circuit air curtain door system.

It has been another objective of this invention to substantially reduce th depth of a closed circuit air curtain door from approximately six feet to approximately one foot and still maintain the penetration resistance and efiiciency of this type of door.

I have accomplished theseobjectives by providing a all) very high velocity and elficient air curtain door system having an automatic mechanism for reducing the velocity of the air stream in the doorway to a value which is not humanly objectionable whenever anyone enters the curtain. In this way, the objection raised by people using a high velocity air door is avoided. The velocity of the curtain is automatically returned to its original high velocity shortly after the person leaves the doorway unless another person immediately enters. In other words, the air curtain has a low velocity so long as there is anyone in the doorway and a high velocity whenever there is no one in the doorway. Surprisingly, this latter situation occurs during a very high percentage of the time. By way of example, it has been estimated that customers are in the doorway of a chain grocery store only 10% of the time and the other 90% of the time, the doorway acts as a temperature wall or barrier. Even if it is assumed that wind conditions will be severe enough to break through the low velocity air curtain 10% of the time, the air door will be open only 1% of the time. This is an improvement of approximately 9% over conventional solid doors.

One of the primary advantages of my invention is that it enables air doors to be added to existing structures without increasing the thickness of the walls and reducing the floor area. In construction of a new structure, standard wall thickness may be used, and thus, the construction costs minimized.

These and other objects and advantages of this invention will become more readily apparent from the following description of the drawings in which,

FIGURE 1 is a perspective view of a doorway, partially broken away, utilizing an air door system constructed in accordance with my invention, 1

FIGURE 2 is a front elevational view, partially broken away and partially in cross-section, of the air door system of this invention,

FIGURE 3 is an enlarged cross-sectional view taken along line 33 of FIGURE 2,

FIGURE 4 is an enlarged cross-sectional view of the velocity control damper, in a fully opencondition,

FIGURE 5 is a view similar to FIGURE 4 but in a partially closed condition, and

FIGURE 6 is a diagrammatic illustration of the electric and hydraulic control circuits for controlling the velocity of air for the curtain.

Referring first to FIGURES 1, 2 and 3 it will be seen that the air door system of this invention includesa doorway 11' of a store front or building 12. This system and its associated duct work is a closed circuit one in which air enters the system through a floor grate or grill 13, and is conveyed through a duct 14, over a heat exchange unit 15, to a blower 16. From the blower 16, theair moves through a duct 17 to a plenum chamber 18 located over the doorway 11. This plenum chamber 18 has a lower outplet opening 19 in the form of a bartype grill or grate through which air is blown downwardly across the doorway 11. The air stream emitted through the grill 19 fans out to form an air curtain 20 directed at the floor grate 13; This grate covers a return air pit 21 and forms a walkway across the doorway sill. From the return pit, air is recirculated through the return duct 14.

The doorway 11 is defined by a pair of vertical door jambs 24 and 25 between which extend a horizontal door frame member 26 and a lower door sill 27. Fitted within the upper door frame member 16 is the bar grate 19 through which the air is emitted from the plenum chamber 18. This grate extends the full width of the doorway. In one preferred embodiment, the grate is six inches, in depth and eight feet in length. Running lengthwise or longitudinally through the grate are'three reinforcing bars 30 which partially obstruct the opening from the plenum chamber through which the air is emitted. These bars occupy approximately one half of the total area of the grill so that the six inch width grill has a total opening approximately three inches in depth and six feet in length. One grill which has been found suitable for this use is manufactured by Barber-Colman Company of Rockford, Illinois and is designated as model STB. v

The floor sill 27 is also partially defined by the lower grill 13. This grill is identical to the upper grill 19 except that it isover twice the depth of the grill 19. In the preferred embodiment it is approximately eighteen inches wide, eight feet in length, and has half of its open i'n'g area occupied by longitudinal bars 31 so that effectively it has an opening of approximately nine inches width and six feet length. Because, the lower grill is over twice as wide as the upper grill, air emitted from the upper grill may be recaptured through the lower one even though it fans out in passing between the two, as shown mos clearly in FIGURE 3.

Conventional sliding doors 32 are located outside the air curtain door and serve as a night lock of the doorway. Of course, any type of night lock door may be utilized, but the sliding door is preferred because of the minimum space itoccupies in the open position.

The heat exchangeunit consists of a conventional heating unit. It, as well as the centrifugal blower or fan 16, is located within an air tight enclosure 33 mounted on the roof 34 of the building of which the doorway 11 forms a part. Of course, the housing 33 could as well be located within the building as outside it.

The system described to this point including the heating unit 15, the blower 16, the duct 17, the upper grill 19, lower grill 13 and return duct 14 form a conventional type of closed circuit air curtain doorway. Theydiffer from the conventional doorway only in that the grill 19 and the lower grill 31 are approximately one-sixth the size of the conventional system. I

Located in the return duct 14 immediately adjacent the heating unit 15 is a two position damper 38. This damper is operative in one position (FIGURE 5) to restrict the flow of air through the return duct 14 to the'heating unit and subsequently to the fan. By retarding the flow of air to the fan, the air supply to the plenum chamber and subsequently through'the grill 19 may be reduced. In a preferred embodiment of this invention, the damper is operative to reduce the flow of air to the blower and subsequently through the outlet grill 19 from approximately 8,000 cubic-feet-p'erminute to approximately 3,000 cubicfeet, per-minute. In other words, the damper of the preferred embodiment effects approximately a 60% reduction in the volume of air emitted from the outlet orifice 19.

The damper 38 may be installed on the exhaust side of the blower in the duct 17 if so desired. However, this location results in a build-up of back pressure on the fan whenever the damper is moved to the partially closed position of FIURE 5. If, however, the damper is located in the return duct 14, closing of the damper'results in a reduction of pressure behind the fan rather than an increase of pressure in front of it so that a smaller fan may be used and a longer expected life achieved from it.

By using a large plenum chamber'of approximately one square foot in cross-section above the grill 19, it has been found that the air curtain may be operated without the use of conventional air directional vanes. If desired, this plenum chamber 18 as well as the ducts 14, 17 may be insulated so as to retard heat loss and minimize the noisiness of the system. Additionally, a thermostat bulb 36 may be installed-in the return duct adjacent the heating and air conditioning unit so as to control the heat exchange unit 15. I I

Referring now to FIGURES 4 and 5, it will be seen that the damper 38 includes four blades or shutters 39 nonrotatably mounted upon shafts 40, 41, 42 and 43 which extend between and are journaled in a rectangular frame -45. A pulley -47 is non-rotatably attached to the protuding ends of each of the shafts 40, 41, 42 and 43 within the air duct 14. The pulleys on the shafts 41 and 42 are double grooved pulleys while the pulleys upon the upper and lower shafts 40, 43 are single grooved. A single endless drive cable 48 extends between these pulleys and crosses between each of them so as to effect an opposing rotation for each succeeding shaft upon rotation of one of the shafts.

The lowermost of the shafts 43 has a control lever 56 keyed to its protruding end and located between the rectangular frame 45 of the damper and the surrounding duct 14. The end 57 of this control shaft is connected to a vertically reciprocal piston rod 58 of a fluid motor 59. Lowering of the rod 58 effects counterclockwise rotation of the lowermost shaft 43 as viewed in FIGURE 4. The counterclockwise rotation of shaft 43 effects clockwise rotation of the shaft 42 as a result of the cross-cable connection between the two pulleys attached to the shaft. Similarly, counterclockwise rotation of shaft 42 results in counterclockwise rotation of shaft 41 and clockwise rotation of shaft 40 because of the cross-cable linkage between the pulleys of each of these shafts. Thus, lowering of the piston rod 58 causes all of the shutters 39 to move from the horizontal position to a position in which they restrict the how of air through the duct 14. In this position of the shutters, approximately a 60% reduction in the velocity of the air stream emitted from the grill 19 is effected. When the control rod 58 is again raised to the position illustrated in FIGURE 4 so as to place the blades in horizontal alignment, the flow of air through the duct 14 is unrestricted with the result that the air flow again rises to the maximum capacity.

The damper 38 described hereinabove is a conventional RotoLink Damper manufactured and sold by American Foundry and Furnace Company of Bloomington, Illinois. Other conventional dampers could be used with the same result; restricting air flow through the duct work to the air outlet grill above the door. The only requirement is that the damper should be very fast acting if it is to operate effectively in this system.

Referring now to FIGURES 2 and 3, it will be seen that an electric eye sender 60 is located on the entrance side of the door'jarnb member 25 and another sender unit 61 is located on the inside ofjthe door. Mounted in alignment with these sender units are a pair of receiver units 62, 63 mounted respectively on the front and rear sides of the'other door jamb member 24. One of the sender units 60 maintains a light beam 64 to one of the receiver units 62 while the other sender 61 is designed to maintain a light beam 65 to the other receiver 63. Upon interruption of either of these light beams, a control system is operative to'actuate the fluid motor 59 so as to affect an immediate reduction in the quantity of air emitted from the air outlet grill 19. Of course, a quantity reduction results in a corresponding velocity reduction. For a given period of time after one of these light beams is broken, the velocity of the air stream emitted from the grill 19 is reduced approximately 60%v so that it is humanly endurable.

The preferred control system includes a timer which is operative to maintain the damper in the closed or restricting position for a preselected period of time after one of the light beams is broken. Thereafter, the motor 59 moves the damper to the open position and steps up the flow of air from the outlet grill 19 to its maximum velocity. This quantity of air in the preferred system is effective to maintain the air curtain 10 under all types of adverse Wind conditions.

Referring now to FIGURE 6, there is shown one form of illustrative diagrammatic electrical and hydraulic control system for efiecting movement of the hydraulic piston rod 58 to open and close the shutters of the dampener 38. As shown in this figure, the light beams 64, 65 are transmitted from the senders 60, 61 connected in series between the main line leads 66, 67. A 15 volt D.C. current is applied across these leads 66, 67. These transmitters 60, 61 are operative to transmit a light beam to the photo cell receivers 62, 63. The receivers 62, 63 are connected in series with a time delay relay TDR-l between leads 66, 67. So long as the light beams from the senders 60, 61 are maintained to the photo cell receivers 62, 63 respectively, a circuit is maintained to the relay TDR-l. However, should either one of these light beams be broken, the circuit to the time delay relay TDR1 is opened and the relay TDR-l de-energized.

Also connected in series across the leads 66, 67 is a normally open contact 68 of relay TDR1 and a coil 70 of solenoid valve 71. So long as the relay TDR1 remains energized, the normally open contact 68 of this relay remains open. However, should either one of the light beams 64, 65 be interrupted by a person or object entering the doorway, the circuit to the time delay relay TDR-l is broken with the result that the normally open contact 68 is closed. Closing of contact 68 results in energization of coil 70 of the solenoid actuated valve 71. Energization of this coil results in movement of the valve to a position in which fluid from an electric motor driven pump 72 flows from the pump outlet 73 through a valve conduit 90 to the hydraulic motor 59 inlet port 91. This fluid causes the piston 76 of motor 59 to move downwardly against the bias of spring 77. As the piston 76 moves downwardly, trapped air in the motor escapes via a tank conduit 78 in the bottom of the motor. The motor port 79 to this conduit is located in the side of the motor above the lowermost position of the piston so that the piston moves past this port and uncovers it whenever the damper is moved to its closed position. As soon as the port 79 is uncovered, fluid from the pump 72 flows continuously through the inlet port 75 of motor 59 and out the tank port 79. In this way, the shutters 39 are held in the closed position.

A predetermined time after the time delay relay TDR-l is de-energized, its circuit is reestablished through the photo cell receivers 62, 63. When this circuit is reestablished, the contact 68 is again moved to its normally open position in which the coil 70 of solenoid valve 71 is deenergized. De-energizatio-n of this coil causes the valve to move to a position in which the fluid motor 59 inlet port 75 is connected via a valve conduit 82 to a tank conduit 83. At this time the pump 72 is connected directly to tank 84 by outlet conduit 73, a valve conduit 85 and a tank conduit 86.

While a diagrammatic illustration of the control circuit has been provided in order to provide a complete disclosure of an operative control system, standard components may be utilized to accomplish the same control function. One standard electric motor, hydraulic, pump and solenoid valve unit suitable for use in a system of this type is a model #lSlOM manufactured by Dor-O-Matic Division of Republic Industries, Inc. This may be connected directly to a model 22DJ2 photoelectric control manufactured by Photoswitch Division of Electronics Corporation of America. These two components may be used to control any type of small hydraulic motor and con-nected damper operator arm. A suitable motor with connected control arm is manufactured by Dor-O-Matic Division of Republic Industries, Inc. and is designated by model #M653.

The operation of the air curtain system illustrated and described hereinabove is as follows: Upon entry of a person into the doorway, one of the light beams 64, 65 between the senders 60, 61 and the photo cell receivers 62, 63 will be broken with the result that the normally energized time delay relay TDR1 will be de-energized. Deenergization of this relay results in closing of the normally open contact 68 and energization of the solenoid coil 70 of solenoid valve 71. This results in the hydraulic motor 59 being actuated so as to cause the shutter con trol arm 56 of the damper 38 to be moved to the position illustrated in FIGURE 5 in which the flow of air into the CJI centrifugal fan 16 is restricted. Restriction of flow of air into the fan causes a decreased volume output from the fan to the plenum chamber over the doorway and thus out of the upper grill 19. The reduced output volume in the air curtain 20 affects approximately a 60% reduction in the velocity of the air stream between the upper outlet grill 19 and the lower floor sill inlet 13. Thus, the velocity of air across the doorway is reduced to something humanly tolerable. The air which passes through the lower floor sill collection grill passes into the return air pit where it is drawn through the return duct 14, past the closed shutters of the dampener and back over the heating and air conditioning system. After the time delay relay TDR-l has been re-energized by reestablishment of the light beams 64, 65 between the senders 60, 61 and the receivers 62, 63 and by expiration of a predetermined time, the contact 68 is again opened and the solenoid coil 70 of solenoid valve 71 deenergiz'ed. This results in upward movement of the piston rod 58 of fl-uid motor 59 to the position illustrated in FIGURE 4 in which all of the shutters are in parallel alignment and provide a minimum obstruction in the duct 14. When flow is unobstructed, a maximum amount of air is permitted to flow to the centrifugal fan 16 and out of the fan to the plenum chamber 18 over the doorway. So long as the dampeners remain in the open position illustrated in FIGURE 4, the maximum capacity of the fan will be emitted through the outlet grill 19 with the result that a high velocity air curtain door will be established between the outlet grill 19 and the collection grill 13.

Throughout this application, I have referred to the volume and velocity of the air curtain as preferably being reduced about 60% upon approach or entry of a person into the doorway. While under most conditions, the 60% reduction has been found to most nearly maximize the efiiciency of the system, those persons skilled in this art will readily appreciate that this reduction may be varied within limits without departing from the spirit of my invention. Specifically, the upper high velocity of the curtain may be increased without departing from an optional lower velocity when a person is in the doorway. Thus, by increasing the upper velocity to a higher than optimal value, while maintaining the lower velocity at an optimal value, the percentage reduction in velocity when a person enters the doorway may be significantly increased without sacrificing anything more than the overall efiiciency of the system. Similarly, by increasing the lower velocity to a greater thanoptim-al value, while maintaining the upper velocity at its most efficient value, the system may be made less comfortable but not intolerable for a person passing through the doorway. Both of these figures may be seaso'nly varied, depending upon wind conditions, climate and other variable conditions. By juggling both the upper and lower velocities, those skilled in the "air curtain art will readily appreciate that the reduction in velocity eflected upon entry of a person into the doorway may be as great as and as low as 30%,while still practicingv my invention and retaining most of the advantages resulting therefrom.

While a preferred embodiment of the invention has been illustrated and described herein, those skilled in the :art to which this invention pertains will readily appreciate numerous changes and alterations which may be made in the system without departing from the scope of the invention. Therefore, I do not intend to be limited except by the appended claims.

Having described my invention, I claim:

1. An air door for a building comprising, an exterior doorway,

a duct system having an inlet end and an outlet end disposed on opposite sides of said doorway for conducting air in a closed circuit path which includes said doorway so as to create an air curtain across said doorway,

means for propelling airthrough said duct system to achieve a predetermined high velocity of said air curtain across said doorway,

temperature control means including heat exchanger means to which the air is subjected as it travels in said duct system to effect a predetermined tem perature change, and

the improvement which comprises means for reduc ing the velocity of said air curtain across said doorway by at least percent but not more than 80 percent of said predetermined high velocity in response to entry of a person into said doorway whereby said air curtain remains intact at a reduced velocity as a person passes through said doorway.

2. An air door system for a building comprising, a doorway,

a duct system having an inlet end and an outlet end disposed on opposite sides of said doorway for conducting air in a closed circuit path which includes said doorway so as to create an air curtain across said doorway, A

means for propelling air through said duct system to achieve a high velocity air curtain across said doorway,

temperature control means including heat exchanger means to which the air is subjected as it travels in said duct system to effect a predetermined temperature change,

movable means for restricting the flow of air in said duct system so as to reduce said high velocity of said air curtain, and

means to efiect movement of. said moveable means to an air flow restricting position in which said high velocity is reduced by atleast 30 percentbut not more than 80 percent in response to entry of a person into said doorway whereby said person in said doorway is subjected to a low velocity air stream while in said doorway and said air curtain remains intact as said person passes through said doorway.

3. An air door for a building comprising, a doorway,

a duct system having an inlet end and an outlet end disposed on opposite sides of said doorway for conducting air in a closed circuit path which includes said doorway so as to create an air curtain across said doorway,

, means forpropeiling air through said duct system to achieve a predetermined high velocity ofsaid air curtain at said duct outlet end, a

temperature control means including heat exchanger means to which the air is subjected as it'travels in said duct system to effect a predetermined temperature change,

, means for detecting the presence of a person as said 7 person approaches said air curtain, and

means operative in responseto said detecting means for reducing the velocity of said air curtain across said doorway by approximately percent prior to the entry of said person into said doorway air curtain and for maintaining said reduced velocity air curtain intact as said person passes through said doorway.

4. An air door for a building. comprising, a doorway,

a duct system having an inlet end and an outlet end disposed on opposite sides of said doorway for conducting air in a closed circuit path which includes said doorway so as to create an air curtain across said doorway,

means for propelling air through said duct system to achieve a predetermined high velocity of said air curtain at said duct outlet end,

temperature control means including heat exchanger means to whichthe air is subjected as it travels in said duct system to effect a predetermined temperaturechan-ge,

means for detecting the presence of a person as said personapproachessaid aircurtain, and

means operative in response to said detecting means for reducing the velocity of said air curtain across said doorway by at least 50 percent but not more than 70 percent prior to the entry of said person into said doorway air curtain and as said person passes through said doorway. 5. The method of establishing and maintaining an air curtain door across an exterior doorway which comprises propelling air from a circulating system through an air outlet on one side of said doorway toward an air inlet on the opposite side of said doorway,

simultaneously drawing air through said air inlet into said circulating system whereby a high velocity stream of air in the form of an air curtain is maintained across said doorway, the improvement which comprises reducing the velocity of said high velocity stream of air by approximately 60 percent upon approach of a person to said door- "way whereby said air curtain is maintained intact at the reduced velocity while the person passes through said doorway. 6. The method of establishing and maintaining an air curtain door across an exterior doorway which comprises propelling air from a circulating system through an air outlet on one side of said doorway toward an air inlet on the opposite side of said doorway,

simultaneously drawing air through said air inlet into said circulating system whereby a high velocity stream of air in the form of an air curtain is maintained across said doorway,

the improvement which comprises reducing the velocity of said high velocity stream of air by at least 30 percent but not more than percent upon approach of a person to said doorway whereby said air curtain is maintained intact at a reduced veiocity as the person passes through said doorway. 7.'The method of establishing and maintaining an air curtain door across an exterior doorway which comprises propelling air from a circulating system through an air outlet on one side of said doorway toward an air inlet on the opposite side of said doorway, simultaneously drawing air through said air inlet into said circulating system whereby a high velocity stream of air in the form of an air curtain is maintained across said doorway, detecting the approach of a person toward said doorreducing the velocity of said high velocity stream of air by at least 30 percent but not more than 80 per- 7 cent in response to the approach of the person to said doorway whereby said air curtain is maintained intact at a reduced velocity as the person passes through said doorway, and

increasing the velocity of said air stream after said person has passed through said doorway so as to reestablish said high velocity air curtain across said dooway.

8. The air door system of claim 2 wherein said restricting means comprises a damper located in said duct system and having a plurality of shutters,

9. The air door system of claim 8 wherein said duct system comprises an inlet duct interconnecting said inlet end and said air propelling means, and an outlet duct interconnecting said outlet end and said air propelling means, said damper being located in said inlet duct whereby said air propelling means is not required to Work against a head of air pressure when said damper is in the air flow restricting position.

10. The air door system of claim 2 wherein said restricting means comprises an air damper and said means to effect movement of said movable means includes a fluid motor for effecting movement of said damper, said system further including an electrical control circuit for controlling the actuation of said fluid motor.

11. An air door system for a building comprising, a doorway,

an air inlet grill located in the floor sill of said doorway,

an air tight housing having a fan located therein, an air inlet duct extending between said air inlet grill and said housing,

an air outlet grill located over the top of said doorsecond duct extending between said fan and said outlet grill,

damper having a plurality of movable shutters located in one of said ducts, said shutters being movable from a first position in which they provide a minimum obstruction to the flow of air in said ducts to a second position in which they partially restrict the flow of air in said ducts and reduce the velocity of air emitted from said outlet grill by at least 30% but not more than 80% first means including an electrical circuit for detecting the approach of a person into said doorway,

means including a fluid motor operable in response to an electrical signal from said first means for moving the shutters of said damper from said first position to said second position, and

means including said motor for returning said shutters of said damper to said first position from said second position after said person has left said doorway.

12. The air door system of claim 11 wherein said means for returning said shutters to said first position in- 10 cludes a time delay element in said electrical circuit.

References Cited by the Examiner UNITED STATES PATENTS MEYER PERLIN, Primary Examiner. 20 W. E. WAYNER, Assistant Examiner. 

5. THE METHOD OF ESTABLISHING AND MAINTAINING AN AIR CURTAIN DOOR ACROSS AN EXTERIOR DOORWAY WHICH COMPRISES PROPELLING AIR FROM A CIRCULATING SYSTEM THROUGH AN AIR OUTLET ON ONE SIDE OF SAID DOORWAY TOWARD AN AIR INLET ON THE OPPOSITE SIDE OF SAID DOORWAY, SIMULTANEOUSLY DRAWING AIR THROUGH SAID AIR INLET INTO SAID CIRCULATING SYSTEM WHEREBY A HIGH VELOCITY STREAM OF AIR IN THE FORM OF AN AIR CURTAIN IS MAINTAINED ACROSS SAID DOORWAY, THE IMPROVEMENT WHICH COMPRISES REDUCING THE VELOCITY OF SAID HIGH VELOCITY STREAM OF AIR BY APPROXIMATELY 60 PERCENT UPON APPROACH OF A PERSON TO SAID DOORWAY WHEREBY SAID AIR CURTAIN IS MAINTAINED INTACT AT THE REDUCED VELOCITY WHILE THE PERSON PASSES THROUGH SAID DOORWAY. 